Screen printers that print solder paste onto a printed circuit board are known (for example, patent literature 1). With this type of screen printer, with a squeegee contacting a screen provided with multiple holes, the screen and the squeegee are moved relatively such that solder paste on the screen is printed onto a circuit board through the holes. Here, the pressing force of the squeegee on the screen affects printing quality.
Specifically, for example, if the pressing force is insufficient, solder paste will be printed in a state raised from the squeegee side openings of the holes provided in the screen, leading to cases in which adjacent solder paste deposits are undesirably connected to each other. To counter this problem, with the screen printer disclosed in patent literature 1, a compression coil spring that biases the squeegee towards the screen is provided between the squeegee and a frame that holds the squeegee, such that printing is not performed with the solder paste raised.
Conversely, if the pressing force is too great, the squeegee slices solder paste entered inside the holes, which may lead to problems such as insufficient printing quantity or lowered longevity of the squeegee or screen. For this problem, the screen printer disclosed in patent literature 1 is provided with a load sensor for detecting the load applied to the squeegee. As a load applied to the squeegee, in addition to the total weight of a member that moves together with the squeegee when the squeegee approaches and separates from the screen, there is the biasing force of the compression coil spring. The screen printer is provided with an air cylinder that acts on the squeegee with a force in a direction against the biasing force of the compression coil spring, with the pressing force being adjusted by controlling the air cylinder pressure based on an output value of a load sensor.